Apparatus for machining balls

ABSTRACT

The specification describes a polishing or lapping machine for steel balls, comprising a stationary disc and a coaxial rotary disc between which the balls are rolled and lapped. The two discs are pressed together by a loading force which is so applied that its line of action intersects a base axis in a specific length of the base axis. The base axis is defined as an axis intersecting the axis of the stationary disc perpendicularly passing through the center of gravity of the stationary disc and through a recess provided in the stationary disc for the introduction and removal of balls. The specific range of the base axis in which the intersection with the line action of the loading force occurs is defined as the range beginning at the center of gravity of the stationary disc and extending away from the center of gravity and away from the recess. With this arrangement of the line of action of the loading force the force exerted on the balls in the working gap between the discs rises from a minimum at the position of entry into the working gap to a maximum value and then decreases to a minimum value again at the position at which the balls are removed from between the discs. The parts adjacent to the ends of the working gaps and adapted to feed balls into the working gap between the discs and receive them as they leave the gap are lined with a shock absorbing wear resistant material such as nylon.

tlnited States Patent 91 Messerschmidt Feb. 12, 1974 APPARATUS FOR MACHINING BALLS [75] Inventor: Klaus Messerschmidt, Schonungen,

Germany [73] Assignee: Sebastian Messer-Schmidt Specialmaschinentabrilt, Schonungen, Germany [22] Filed: Sept. 13, 1971 [21] Appl. No.: 179,694

[30] Foreign Application Priority Data Oct. [5, 1970 Germany 2050662 [52] U.S. Cl. 51/117, 51/130, 51/289 S [51] Int. Cl B24b 5/20 [58] Field of Search. 51/116, 117, 130, 128, 3,161, 51/289, 289 S [56] References Cited UNITED STATES PATENTS 2,944,375 7/1960 Lipkins 51/117 3,250,042 5/1966 Messerschmidt 5l/ll6 Primary Examiner-Harold D. Whitehead Assistant Examiner-Nicholas P. Godici [57] ABSTRACT The specification describes a polishing or lapping machine for steel balls, comprising a stationary disc and a coaxial rotary disc between which the balls are rolled and lapped. The two discs are pressed together by a loading force which is so applied that its line of action intersects a base axis in a specific length of the base axis. The base axis is defined as an axis intersecting the axis of the stationary disc perpendicularly passing through the center of gravity of the stationary disc and through a recess provided in the stationary disc for the introduction and removal of balls. The specific range of the base axis in which the intersection with the line action of the loading force occurs is defined as the range beginning at the center of gravity of the station ary disc and extending away from the center of gravity and away from the recess.

With this arrangement of the line of action of the loading force the force exerted on the balls in the working gap between the discs rises from a minimum at the position of entry into the working gap to a maximum value and then decreases to a minimum value again at the position at which the balls are removed from between the discs.

The parts adjacent to the ends of the working gaps and adapted to feed balls into the working gap between the discs and receive them as they leave the gap are lined with a shock absorbing wear resistant material such as nylon.

12 Claims, 9 Drawing Figures PATENIEUFEB 12 I974 3.791. 083

sum 1 0f 3 mmvroa KLRUS MESSERSCHMIDT PATENIEmEmmM 8.791.083

SHEET 2 [IF 3 INVENTOR. Kmu s MESSER. s CHMID? BY WW, m8 W PATENTEDFEB 12 m4 SHEET 3 BF 3 INVENTOR. Klnus MEssE RSGH MIDT Ar on 54 APPARATUS FOR MACHINING BALLS BACKGROUND OF THE INVENTION 1. Field to which Invention Relates The present invention relates to apparatus for machining balls, and more particularly to such apparatus for grinding and lapping of balls between a rotating disc and a stationary disc, which is provided with a sectorlike recess, into which a stripper extends on whose one side the balls, for example from a magazine, are introduced into the working gap between the discs and on the other side the machined balls are removed from the working gap, means being provided for exerting an axial pressure on the stationary disc.

2. The Prior Art Lapping machines of this type are known. Some machines operate with a vertical axis and some with a horizontal axis. However, apparatus with an oblique axis of the lapping discs is conventional. The magazines used may be in the form of drums, elevators or, preferably, an annular magazine surrounding the lapping discs. This annular magazine rotates in a direction of movement opposite to the direction of the lapping disc and discharges the balls to be machined the one side of the stripper. After the balls have run through the working gap between the lapping discs, they are removed on the other side of the stripper by the magazine.

Various means have been provided to grind or lap or polish the balls to the closest possible tolerances without out it being possible to prevent the balls being damaged on being introduced into the working gap and on being removed from it. This is primarily due to the fact that in the case of conventional devices the pressure exerted on the stationary lapping disc acts on the center of the lapping disc. Owing to the sector-shaped recess of this disc is the difficulty that its position adjacent to the ball inlet and ball outlet a particularly high surface pressure is brought to bear on the discs. This pressure decreases continuously approximately towards the middle of the path through which the balls pass between the discs and reach a minimum at this position. Owing to the sudden and forceful] pressure developing at the ball inlet the balls are excessively loaded. At the outlet they are frequently thrown out at a high speed so that they strike against other balls which have already been ejected.

. SUMMARY OF THE INVENTION These phenomena are avoided by the invention in two different ways. Firstly, the point of engagement of the pressure on the stationary disc lies on an axis running through the center point and the recess in the disc at the position of the center of gravity of the stationary disc or, looking from the direction of the recess, lies outside this center of gravity and the surface loading acting on the balls located in the working gap firstly rises in a direction leading away from the ball inlet to a maximum and from this maximum continuously decreases towards the ball outlet. The curve of area or surface area loading can be symmetrically curved but it is also possible for it to have a straight line part in its central zone, corresponding to the maximum surface area loading.

Owing to the feature in accordance with the invention an extremely gentle treatment or processing of the balls is achieved on their passage between the lapping discs, and the application of force via the discs occurs incrementally and decreases in the same manner so that the balls are placed in and taken from the working gap in a gentle manner. In extreme cases, that is to say when the point of engagement of the pressure lies in the center of gravity of the stationary disc, the same surface loading acts practically on the balls from the inlet to the outlet. Apart from the improved processing or machining of the balls the measure in accordance with the invention leads to a more even wear of the lapping discs.

The distance by which the point of engagement of the pressing force must be placed beyond the center of gravity of the stationary disc provided with the sectorshaped recess depends upon the size of the respective recess and the diameter of the disc.

A further measure, which serves in a similar manner for attaining the purpose of the invention resides in that the ball inlet on the one hand of the stripper and the ball outlet on the other side of it are lined with a shock absorbing wear resistant material. This feature in itself leads to a more gentle treatment of the balls at the inlet and the outlet, that is to say in zones where the balls often pile up and consequently may strike against one another. A material which has been found particularly suitable for the lining is polyamide or another material with similar properties.

In accordance with a further feature of the invention the lining of the wall which lies foremost in turns of the direction of rotation of the rotating disc, of the ball inlet and the ball outlet comprise shoes covering the respective disc, and between the free end of the respective shoe and the lining of the respective rear wall an inlet or outlet gap for the balls is arranged. If the balls in the case of such an apparatus pass into the ball outlet or ball inlet, they do not lie, as is the case with the known apparatus, on the rotating disc, but come to rest on a stationary surface of shock absorbing material, so that, in conjunction with the gentle introduction and removal of the balls from the working gap an extremely gentle treatment of the balls is assured. The balls can then be ground, polished or lapped with the highest degree of accuracy and the minimum expense.

In accordance with a further feature of the invention in the upper cover, forming the inlet and the outlet gap, of the lining guide grooves are arranged in an array, corresponding to the grooves of the discs. Owing to this the balls are introduced as planned into the working gap between the two discs, so that they pass directly into the grooves of the working gap.

In accordance with a further feature of the invention the inlet gap and the outlet gap are both arranged as an acute angle between the discs and with the apex of the angle directed against the direction of rotation of the rotating disc. Owing to this in the ball inlet the balls roll against the direction of movement of the rotating disc into the working gap, but this rolling down movement of the balls corresponds to their rolling movement in the working gap between the two discs. There is therefore no forced reversal of movement, which afterwards leads to an excessively strong grinding action on the surface of the balls. On the other hand, the outlet gap runs in the direction of movement of the disc and thus in the direction of movement of the balls so as to rise slightly onto the shoe covering the disc in the ball outlet.

It has been found particularly convenient if the shoe of the ball inlet has grooves on its underside in array corresponding to the grooves of the discs for the passage of the balls introduced. This is in accordance with the further feature that the balls are guided by the guide grooves of the entry gap directly into the grooves of the working gap between the discs.

In accordance with a further feature of the invention the shoe of the lining of the ball outlet has fingers fitting into the grooves at the free end of the shoe. These fingers pass underneath the balls which arrive and move them gently out of the grooves and the ball outlet.

In accordance with the invention the lining having the shoe, of the ball inlet can be caused to vibrate or oscillate in a direction perpendicular to the direction of rotation of the disc by means of a suitable oscillating drive, for example a bob-weight or eccentric drive to an oscillating magnet. Owing to this feature the balls passing into the ball inlet, for example from a magazine, can be transported as far as to the radially inner end of the ball inlet without any jamming occurring which would lead to damage of the balls. The balls are thus guided as far the radially innermost groove of the lapping discs so that all grooves are evenly loaded with the balls to be worked.

LIST OF SEVERAL VIEWS OF DRAWINGS Further features, details and advantages of the invention will appear from the following description of the preferred embodiment of the invention and with reference to the drawings.

FIG. 1 shows a grinding an lapping device diagrammatically and in axial section.

FIG. 2 is a plan view of the two discs and the magazine of the apparatus in accordance with FIG. 1.

FIGS. 3, 4 and 5 show three graphs of the area loading in the case of various points of engagement of the pressure.

FIG. 6 is a section through the ball inlet and outlet generally on the line VIVI of FIG. 7.

FIG. 7 is a section through the ball inlet and outlet generally on the line VIIVII of FIG. 6.

FIG. 8 is a section through the ball inlet generally on the line VlII-VIII.

FIG. 9 is a section through the ball outlet generally on the line IX--IX, both in FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS In the case of the apparatus diagrammatically shown in FIG. 1 the lapping discs, that is to say the rotating lower disc 1 and the stationary upper disc 2 are arranged with a vertical axis. The lower disc 1 is carried by a support plate 3 which is fixed to the shaft 4 driven via a bevel gearing 5 and the V-belt drive 6 by the electric motor 7. The upper disc 2 is fixed to the support plate 8. Between the latter and the pressure plate 9 pressure springs 10 are arranged in a circular arrangement, which transfer the pressure, exerted by the piston rod 11 of the pressure motor 12 to the upper disc 2. The two concentrically arranged lapping discs 1, 2 are surrounded by an annular magazine 13 in an eccentric arrangement. The magazine is driven by the motor 14, whose drive pinion 15 meshes with the gearing 16 on the lower side of the magazine 13. The direction of movement 17 of the rotating magazine 13 is opposite to the direction of movement 18 of the rotating disc 1.

The upper disc 2 has a sector-like recess 19, which in the case of the embodiment of the invention shown defines an angle of approximately 45. This angle can, however, be larger or smaller without having any influence on the invention. Owing to this recess 19, which serves for the introduction and removal of balls, the center of gravity 20 of the upper disc 2 is displaced on the axis 26, determined by the recess 19 and the center point 21 of the discs 1 and 2, by the distance x. If the center of the pressure acting on the upper disc 2 were to lie in the center point 21 of the disc, the pressure diagram or graph in accordance with FIG. 3 would result. In this case the passage of the balls through the working gap 22 between the two discs 1 and 2 from the ball inlet 23 to the ball outlet 24 is represented on the horizontal axis of the graph, while the vertical axis denotes the specific pressure or pressure per unit surface area exerted by the disc 2 on the balls 25. Owing to the slight oblique angle of the surface 27 at the ball inlet of the disc 2 the pressure p in this zone 5, rises from zero to a maximum. Then the specific pressure decreases as far as the apex 28 of the curve and from this position increases to the maximum again at the ball outlet. At the position adjacent to the oblique surface 27 at the ball outlet of the stationary disc 2 it then sinks again along the path s to zero.

If the point of engagement of the pressure on the stationary disc 2 in the center of gravity 20 displaced on the axis 26 by the recess 19 there results a surface loading in accordance with the graph or diagram of FIG. 4 with a constant presusre p from the ball inlet to the ball outlet. The further the point of engagement of the pressure is displaced along the axis 26 beyond the center of gravity 20, for example by the distance y at point 29, the more the curve of surface loading becomes arched towards the bottom. The result is a more gentle engagement of force at the zone of the ball inlet 23 and also a more gentle exit of the balls at the ball outlet 24, while between these two limits the surface loading increases continuously as far the apex point 28 and after this continuously sinks in a similar manner. This results not only in a more gentle treatment of the balls, more particularly at the inlet into the working gap 22 and of the outlet leading out of it, but also to a more even wear of the lapping discs.

At the point of engagement between the magazine 13 and the sector-shaped recess 19 of the stationary disc 2 there is an approximately radially extending stripper 30, which extends transversely through the magazine 13 and through the recess 19. Owing to the presence of suitable guide surfaces 31 this stripper passes the balls 25 on the one side into the ball inlet 23 and on its other side passes them out of the ball outlet 24. The ball inlet 23 and the ball outlet 24 are provided with a lining 33, 34, 35, 36 of shock absorbing and wear resistant material such as polyarnide, both on the side of the stripper 30 and also on the side of the side walls 32 of the stationary disc 2. The linings 33,35, which in terms of the direction of rotation 18 of the lapping disc 1 lie to the front are provided with a shoe 37 and 38 respectively which covers the bottom of the ball inlet 23 and the ball outlet 24 and together with a lining 34 and 36 respectively lying to the rear forms an inlet gap 39 and an outlet gap 40 respectively for the balls. In this respect in the respective upper cover forming the inlet and outlet gap 39 and 40 respectively guide grooves 41 and 42 respectively are provided. These grooves have an arrangement corresponding to that of the grooves 43 of the rotating disc 1 and of the stationary disc 2 respectively. In a corresponding manner on the lower side 44 of the shoe 37 in the ball inlet 23 grooves 45 are provided through the passage of balls 25 introduced into the working gap 22.

The inlet gap 39 between the two linings 33 and 34 and also the outlet gap 40 between the two lines 35 and 36 both running in the same direction as an acute angle to the plane of the discs 1 and 2 and with the apexal angle oppositely to the direction of rotation of the disc 1. For the inlet gap 39 this means that balls 25, which roll down over the oblique face 46 of the shoe 37 in the direction of the arrow 47 can maintain the same direction of movement as soon as they strike the rotating disc 1 and are entrained by it. The introduction of the balls 25 is thus carried out in a very gentle manner. As regards the outlet gap 40 there is an unhindered exit of the balls in a direction of movement. In this respect of the removal of the machined balls 25 is aided by fingers 48 arranged on the free end of the shoe 38. These fingers fit into the grooves 43 of the rotating disc 1 and lift the balls out of them.

A particular form of the embodiment, in accordance with FIGS. 6 and 7, incorporates an oscillating drive 49 arranged to act upon the lining 33, of the ball inlet 23, arranged on the shoe 37. This oscillatory drive can for example be a bob-weight or eccentric drive or incorporate an oscillating magnet, which brings about movement of the lining 33 and, more especially, its shoe 37 so that the balls entering in a direction of the arrow 50 from the magazine 13 into the ball inlet 23 are transported as far as the outer end 51 of the small inlet 23 so that an even loading of the grooves 43, 45 of the working gap 22 between the discs 1 and 2 is ensured.

I claim:

1. In an apparatus for machining balls in continuous operation comprising:

a rotary disc,

means for rotating the rotary disc,

a stationary disc generally coaxial to the rotary disc and having a sector-like recess, the two discs defining therebetween a working gap,

a stripper extending into the recess,

means for supplying balls to an inlet side of the stripmeans for receiving balls from an outlet side of the stripper after they have been machined by being rolled against the stationary disc while moving from the inlet to the outlet side of the stripper in the working gap between the discs, and

means pressing the discs towards each other in the axial direction by applying a force whose line of action intersects a base axis, said base axis being an axis which perpendicularly intersects the common axis of the discs, passes through the center of gravity of the stationary disc and runs through the recess,

the improvement which resides in that the abovementioned line of action intersects the base axis at a point lying at a predetermined distance from the common axis, said distance from the common axis extending along the base axis from the center of gravity of the stationary disc in a direction away from the center of gravity and from the recess .so that the pressure exerted on the balls is such that it increases from a minimum value at their point of entry into the working gap between the discs to a maximum value and then decreasing again to a low value at the outlet side of the stripper.

2. The apparatus of claim 1 further comprising a lining of a wear resistant, impact absorbing plastic material on the inlet side of the stripper for holding the balls before they pass into the working gap between the discs, and a lining of wear resistant, impact absorbing plastic material on the outlet side of the stripper for receiving balls from the working gap.

3. In an apparatus for machining balls in continuous operation comprising:

a rotary disc,

means for rotating the rotary disc,

a stationary disc generally coaxial to the rotary disc and having a sector-like recess, the two discs defining therebetween a working gap,

a stripper extending into the recess,

means for supplying balls to an inlet side of the stripper,

means for receiving balls from an outlet side of the stripper after they have been machined by being rolled against the stationary disc while moving from the inlet to the outlet side of the stripper in the working gap between the discs, and

means pressing the discs toward each other in the axial direction by applying a force whose line of action intersects a base axis, said base axis being an axis which perpendicularly intersects the common axis of the disc, passes through the center of gravity of the stationary disc and runs through the recess,

the improvement which resides in that the apparatus comprises a lining of a wear resistant, impact absorbing plastic material on the inlet side of the stripper for holding the balls before they pass into the working gap between the discs, and a lining of wear resistant, impact absorbing plastic material on the outlet side of the stripper for receiving balls from the working gap,

the above-mentioned line of action intersects the base axis at a point lying at a predetermined distance from the common axis, said distance from the common axis extending along the base axis from the center of gravity of the stationary disc in a direction away from the center of gravity and shoes forming part of the respective linings and extending over the surface of the rotary disc, the shoes having free ends adjacent to further parts of the linings which define entry and outlet gaps for the balls.

4. The structure as set forth in claim 3, in which the parts of the linings which cooperate with the shoes in forming the gaps are provided with ridges which are arranged .so as to correspond with ridges on the rotary disc.

5. The structure as set forth in claim 4, in which the ball entry gap and also the ball outlet gap between the shoes and parts of the lining are aligned with planes de fining an acute angle to the plane of the discs, the angles being directed against the direction of rotation of the rotary disc.

6. The structure as set forth in claim 4, in which the shoe on the inlet side of the stripper possesses grooves on its underside in an arrangement corresponding to grooves in the discs for the passage of the balls introduced into the gap between the discs.

7. The structure as set forth in claim 6, in which the shoe of the lining on the outlet side of the stripper has fingers fitting into grooves of the rotating disc.

8. The structure as set forth in claim 7, further comprising an oscillatory drive for causing the lining on the ball inlet side to vibrate.

9. An apparatus for machining balls in continuous operation, said apparatus comprising in combination:

a first and a second disc disposed in coaxial super imposition spaced apart to define a working gap therebetween, the first disc being rotatably mounted, and the second disc being rotatably stationary but axially displaceable towards the first disc,

driving means coacting with the first disc for rotating the same,

pressure means coacting with the second disc for supplying thereto an axially directed pressure towards the first disc,

an inlet means communicating with said working gap for feeding balls to be machined into the same, an outlet means communicating with the working gap at a point circumferentially spaced from the inlet means for discharging machined balls from the gap,

the center of gravity of the second disc being eccentrically disposed with reference to the center axis of said second disc and the pressure being applied to the second disc at a point along a line joining the center of gravity of the second disc and the geometric center of said second disc, said point being eccentric by a distance such that the working pressure exerted by the second disc upon the balls in the working gap increases from a minimum pressure at the inlet means to a maximum pressure intermediate the inlet and the outlet means and decreases from said maximum pressure to a minimum pressure at said outlet means.

10. The apparatus according to claim 9, wherein the first disc is a lower disc and the second disc is the upper disc.

11. The apparatus according to claim 9 wherein said second disc includes a sector shaped recess, said inlet and outlet means being located in said recess.

12. The apparatus according to claim 9 wherein said pressure means includes spring means and a pressure plunger, said spring means transmitting the pressure exerted by the plunger to the second disc. 

1. In an apparatus for machining balls in continuous operation comprising: a rotary disc, means for rotating the rotary disc, a stationary disc generally coaxial to the rotary disc and having a sector-like recess, the two discs defining therebetween a working gap, a stripper extending into the recess, means for supplying balls to an inlet side of the stripper, means for receiving balls from an outlet side of the stripper after they have been machined by being rolled against the stationary disc while moving from the inlet to the outlet side of the stripper in the working gap between the discs, and means pressing the discs towards each other in the axial direction by applying a force whose line of action intersects a base axis, said base axis being an axis which perpendicularly intersects the common axis of the discs, passes through the center of gravity of the stationary disc and runs through the recess, the improvement which resides in that the above-mentioned line of action intersects the base axis at a point lying at a predetermined distance from the common axis, said distance from the common axis extending along the base axis from the center of gravity of the stationary disc in a direction away from the center of gravity and from the recess so that the pressure exerted on the balls is such that it increases from a minimum value at their point of entry into the working gap between the discs to a maximum value and then decreasing again to a low value at the outlet side of the stripper.
 2. The apparatus of claim 1 further comprising a lining of a wear resistant, impact absorbing plastic material on the inlet side of the stripper for holding the balls before they pass into the working gap between the discs, and a lining of wear resistant, impact absorbing plastic material on the outlet side of the stripper for receiving balls from the working gap.
 3. In an apparatus for machining balls in continuous operation comprising: a rotary disc, means for rotating the rotary disc, a stationary disc generally coaxial to the rotary disc and having a sector-like recess, the two discs defining therebetween a working gap, a stripper extending into the recess, means for supplying balls to an inlet side of the stripper, means for receiving balls from an outlet side of the stripper after they have been machined by being rolled against the stationary disc whilE moving from the inlet to the outlet side of the stripper in the working gap between the discs, and means pressing the discs toward each other in the axial direction by applying a force whose line of action intersects a base axis, said base axis being an axis which perpendicularly intersects the common axis of the disc, passes through the center of gravity of the stationary disc and runs through the recess, the improvement which resides in that the apparatus comprises a lining of a wear resistant, impact absorbing plastic material on the inlet side of the stripper for holding the balls before they pass into the working gap between the discs, and a lining of wear resistant, impact absorbing plastic material on the outlet side of the stripper for receiving balls from the working gap, the above-mentioned line of action intersects the base axis at a point lying at a predetermined distance from the common axis, said distance from the common axis extending along the base axis from the center of gravity of the stationary disc in a direction away from the center of gravity and shoes forming part of the respective linings and extending over the surface of the rotary disc, the shoes having free ends adjacent to further parts of the linings which define entry and outlet gaps for the balls.
 4. The structure as set forth in claim 3, in which the parts of the linings which cooperate with the shoes in forming the gaps are provided with ridges which are arranged so as to correspond with ridges on the rotary disc.
 5. The structure as set forth in claim 4, in which the ball entry gap and also the ball outlet gap between the shoes and parts of the lining are aligned with planes defining an acute angle to the plane of the discs, the angles being directed against the direction of rotation of the rotary disc.
 6. The structure as set forth in claim 4, in which the shoe on the inlet side of the stripper possesses grooves on its underside in an arrangement corresponding to grooves in the discs for the passage of the balls introduced into the gap between the discs.
 7. The structure as set forth in claim 6, in which the shoe of the lining on the outlet side of the stripper has fingers fitting into grooves of the rotating disc.
 8. The structure as set forth in claim 7, further comprising an oscillatory drive for causing the lining on the ball inlet side to vibrate.
 9. An apparatus for machining balls in continuous operation, said apparatus comprising in combination: a first and a second disc disposed in coaxial super imposition spaced apart to define a working gap therebetween, the first disc being rotatably mounted, and the second disc being rotatably stationary but axially displaceable towards the first disc, driving means coacting with the first disc for rotating the same, pressure means coacting with the second disc for supplying thereto an axially directed pressure towards the first disc, an inlet means communicating with said working gap for feeding balls to be machined into the same, an outlet means communicating with the working gap at a point circumferentially spaced from the inlet means for discharging machined balls from the gap, the center of gravity of the second disc being eccentrically disposed with reference to the center axis of said second disc and the pressure being applied to the second disc at a point along a line joining the center of gravity of the second disc and the geometric center of said second disc, said point being eccentric by a distance such that the working pressure exerted by the second disc upon the balls in the working gap increases from a minimum pressure at the inlet means to a maximum pressure intermediate the inlet and the outlet means and decreases from said maximum pressure to a minimum pressure at said outlet means.
 10. The apparatus according to claim 9, wherein the first disc is a lower disc and the second disc is the upper disc.
 11. The apparatus according to claim 9 wherein said second dIsc includes a sector shaped recess, said inlet and outlet means being located in said recess.
 12. The apparatus according to claim 9 wherein said pressure means includes spring means and a pressure plunger, said spring means transmitting the pressure exerted by the plunger to the second disc. 